RemoteObjectsUpsertDemo.page

<apex:page standardController="Account" showHeader="true" sidebar="false" id="page">
    
    <apex:include pageName="RemoteObjectsUpsertRemote" />
    
    <div id="vf-page">
        <apex:form id="form">
            <apex:inputText value="{!Account.Name}" id="accountName"/>
            <apex:commandButton value="Upsert" onclick="return upsertAccount('{!Account.Id}', '{!$Component.accountName}');" />
        </apex:form>
    </div>
     
    <apex:include pageName="RemoteObjectsUpsertScript" />
</apex:page>

RemoteObjectsUpsertRemote.page

<apex:page >
    <apex:remoteObjects >
        <apex:remoteObjectModel name="Account" fields="Id" />
    </apex:remoteObjects>
</apex:page>

RemoteObjectsUpsertScript.page

<apex:page >
    <script type="text/javascript">
        function upsertAccount(prmAccountId, prmAccontName) {
            var accountName = document.getElementById(prmAccontName).value;
            
            var account = new SObjectModel.Account();
            if (prmAccountId) {
                account.set('Id', prmAccountId);
            }
            account.set('Name', accountName);
            
            account.upsert(function(err, results, event) {
                if (err) {
                    alert(err.message);
                } else {
                    console.log(results);
                }
            });
            
            return false;
        }
    </script>
</apex:page>